Atomization is the dominant method for producing metal and pre-alloyed powders from aluminum, iron, low-alloy steels, stainless steels, tool steels, titanium and superalloys, among others. Although there is a great diversity of methods, processes and techniques of atomization, particularly water and gas atomization have continued to dominate the production of high melting point metallic powders. Both techniques are relatively simple to implement but with lower energy efficiency, in addition to the well-known features of the produced powder; e.g. irregular shape, low surface quality, relative high internal porosity, relative wide particle size distributions (high geometric standard deviation σg, around 2.0-2.3), etc. On the other hand, other techniques, such as the centrifugal atomization (CA) exhibits, under certain process conditions, a higher energy efficiency with an outstanding powder quality. However, such type of processes are often technically more complex than the previous aforementioned techniques. The centrifugal melt atomization of metals is a liquid metal-fed physical method to produce powders, where a liquid stream of molten metal is poured onto a rotating disk or similar and it is broken and dispersed, under the action of centrifugal forces, into a fine powder particulate matters that subsequently solidify in contact with the atmosphere. The potential of centrifugal atomization techniques, especially for industrial applications, is not fully developed due to the lack of in-depth scientific understanding of the physical process of atomization and lack of reliable designs.
Traditionally, tool steel powders are produced by gas or water atomization methods. In general terms, water atomized tool steel powders exhibit irregular shaped particles and are suitable for die compaction and sintering to higher theoretical density. Although gas atomized tool steel powders exhibit spherical or near-spherical particles with high apparent densities, which thus may requires hot or cold isostatic pressing consolidation. The key factor of powder metallurgy of tool steels is based mainly on the uniform microstructure that can be obtained, compared to forged and conventionally produced products, and the higher homogeneity in its chemical composition. This situation, for example, leads to excellent values of toughness and less distortion during heat treatment, redounding in an increase of the tool service life.
Although, centrifugal atomization is conducted for producing a variety of metals and metallic alloys in commercial, near-commercial, laboratory and small pilot plant scales, surprisingly this technique has not been fully and broadly developed for mass production of iron-based alloys. CA is applied on an industrial scale for numerous singular applications, particularly for alloys presenting lower melting temperatures; thus the problems of erosion of the rotating element do not present a critical technical challenge. Ti, Ni, Fe and others . . . generic trough proper atomizing rotating element configuration, some concrete alloys with almost any atomizing rotating element configuration, but taking other parameters into account. However, and contrary to what has been observed and mentioned, the present inventors have found that, taking certain precautions, the centrifugal atomizing rotating element technique is suitable for the production of some steel powder, especially tool steel powder, high strength steels and other iron-based alloys of similar properties. Also, the inventors show that the atomization technique can be turned into the most economical; achieving the desired specifications of the iron-based powders and saving a large amount of energy and associated costs.